1. Field of the Invention
The present invention relates to vertically oriented glass furnaces which have been useful for producing spheroidal glass particles, and methods of operation of such furnaces.
2. Brief Description of the Related Art
Commercial glass particles typically are available in sizes of 10 micrometers to 50 micrometers. They have wide applications such as in electronics, as a reflecting material used in paints (e.g., road signs, roadmarkings), construction material for runways (night landing strips), for grinding/sand blasting applications, injection molding of plastics, etc.
The glass beads are formed by a variety of methods (see, e.g., U.S. Pat. No. 4,961,770). In some cases, electrical and magnetic fields are used for breaking up molten glass streams into large particles and then injecting these particles within the core of a burner flame. The softened glass beads in the high temperature flame zone react and, due to surface tension, form into glass spheres of very small sizes (10 to 50 micrometers).
In many cases, a very large furnace (e.g., a water or air-cooled vertical reactor) is used for glass bead production (see, e.g., U.S. Pat. No. 4,046,548). As shown in FIG. 1 herein, the raw material R, which can include crushed glass or cullet in powder form, is fed by devices 110 from a raw material hopper 108 above the air-fuel burner flame region of the vertical reactor 102 of a typical vertical glass furnace 100. The combustion gas stream, which is traveling upwards, immediately entrains the raw material. The suspended glass particles in the high temperature combustion zone soften and, due to surface tension over the glass surface, form into tiny spheres. An average size of the resulting glass particles is dictated by the effective terminal velocity (and therefore residence time) of the particle and the average temperature of the surrounding combustion gases. It can be very important to maintain a uniform temperature profile in the furnace gases to produce a required size distribution for the final glass product.
The flame gases, and entrained air Ai from open bottom 122 typically above a floor or ground 124, carry glass particles upward and, upon completion of spheroidizing process, they settle in a large furnace portion 104. The final product P is then conveyed along a product discharge path 120 to a sizing process, where proper size product is packed for shipment. In many cases, about 10% to 15% product remains with the furnace exhaust gas passing through flue 106, which requires additional separation process such as cyclonic separation, a bag house, or electrostatic precipitator (ESP), generally designated 114. Cleaned flue gases leave the separator at a stack 118.
As illustrated in FIG. 1, the recovered product PR from the bag-house, etc. 114 is typically recycled to the reactor 102 along a path 116. The furnace can typically process anywhere from 1000 lb/hr (453.6 kg/hr) to 10,000 lb/hr (4,536 kg/hr) of product, depending on the size. The air-fuel burners 112 generally produce a well-mixed bluish flame, which does not have much, if any, visible radiation. This flame also creates outside air infiltration (as shown in FIG. 1) Ai. The ambient air dilution lowers the average flame gas temperature, but increases overall combustion gas volume. This air infiltration causes two effects as far as the process is concerned:
In most cases, the furnace reaches a performance bottleneck, where the maximum raw material feed capacity is reached based on furnace diameter, overall length, total burner firing rate, and outside air entrainment. If additional raw material is added, the spherodizing process is negatively affected and the product quality can degrade and becomes an issue. Here, the product starts agglomerating in lumps due to poor heat transfer, insufficient entrainment, or due to localized hot-spots in the furnace. Most furnace operators therefore do not exceed furnace production capacity due to quality concerns. A need therefore remains to improve vertical glass furnace production levels while permitting glass quality to be retained.
According to a first aspect of the present invention, a process of operating a vertical glass bead furnace, the furnace including a shaft open at the bottom, a raw material addition device, and an air-fuel burner, comprises the steps of firing the air-fuel burner and thereby entraining air into the furnace shaft through the open bottom of the shaft, adding raw material into the furnace, and an additional step selected from the group consisting of: (a) injecting oxidant into the shaft adjacent to the shaft bottom using a single lance, (b) operating an oxy-fuel burner in the shaft adjacent to the shaft bottom, (c) injecting oxidant into the shaft adjacent to the shaft bottom using multiple lances, (d) injecting oxidant into the shaft using a lance incorporated into the air-fuel burner, and (e) injecting oxidant into the shaft adjacent to the shaft bottom using an oxidant injection ring.
According to another aspect of the present embodiment, a vertical glass furnace comprises a shaft having an interior space and open at the bottom, a raw material addition device mounted so add raw material to the interior of the shaft, an air-fuel burner, and an additional device selected from the group consisting of: (a) a single oxidant injection lance adjacent to the shaft bottom useful for injecting oxidant into the shaft, (b) an oxy-fuel burner in the shaft adjacent to the shaft bottom, (c) multiple oxidant injection lances adjacent to the shaft bottom useful for injecting oxidant into the shaft, (d) a lance incorporated into the air-fuel burner, and (e) an oxidant injection ring positioned for injecting oxidant into the shaft adjacent to the shaft bottom.
Still other objects, features, and attendant advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description of embodiments constructed in accordance therewith, taken in conjunction with the accompanying drawings.